Clean coal technology microbial wash

ABSTRACT

Described herein are methods, apparatuses, and systems for reducing the sulfur content of coal. Coal is loaded into an apparatus comprising a vertically rotatable drum within a housing. The rotatable drum comprises a perforated cylindrical outer wall, a solid cylindrical inner wall, and a perforated, cylindrical central wall positioned between the outer wall and the inner wall, wherein the coal is loaded into a coal wash annulus between the central wall and the outer wall. A microbial wash fluid flows into a wash fluid annulus between the inner wall and the central wall, wherein the microbial wash fluid contains sulfur digesting bacteria and nutrients for the bacteria. The drum is rotated to cause the microbial wash fluid to migrate from the wash fluid annulus through the coal in the coal wash annulus and collect in a splash wash annulus between the outer wall and the housing.

INCORPORATION BY REFERENCE

The present patent application claims priority to the Provisional patent application identified by U.S. Ser. No. 62/158,672, filed May 8, 2015, titled “Clean Coal Technology Microbial Wash”, the entire contents of which are hereby incorporated herein by reference.

BACKGROUND OF THE INVENTIVE CONCEPTS 1. Field of the Inventive Concepts

The presently disclosed inventive concept(s) relates generally to fossil fuel desulfurization devices and methods and, more particularly, but not by way of limitation, to devices, systems and processes for removing sulfur from coal.

2. Brief Description of Related Art

Due to environmental concerns, there is increasing need to reduce sulfur emissions from the burning of fossil fuels, and particularly from the burning of coal. In coal combustion to generate electric power and process heat, sulfur contaminants in the coal are emitted as SO₂, which is seen as one of the main causes of acid rain.

Sulfur in coal exists in inorganic and organic forms. Inorganic sulfur is mostly pyritic sulfur, generally iron sulfide, and is present as a separate mineral phase dispersed within the coal. Pyritic sulfur can usually be removed from the coal by physical cleaning. Organic sulfur (i.e., sulfur covalently bound to carbon or a hydrocarbon moiety) can potentially be removed using chemical and biological cleaning methods, but these methods have not yet been commercialized.

In-bed desulfurization involves the use of a calcium-based sorbent such as limestone, which captures the SO₂ as it is emitted during fluidized bed combustion. The technology has a number of technical and economic difficulties including inefficient use of limestone and erosion of in-bed heat-exchanger tubes. The most common method for removing sulfur is flue gas desulfurization. This post-combustion method typically uses wet scrubbers with limestone or wet lime to remove the sulfur as gypsum.

Logistic problems associated with disposing of large volumes of gypsum at power generation sites create difficulties with post combustion sulfur removal. However, the complete removal of sulfur at mine sites is difficult due to difficulties removing organic sulfur. There remains a need for economical and efficient methods for removing both inorganic and organic sulfur from coal prior to combustion of the coal.

SUMMARY OF THE DISCLOSURE

In general, described herein are apparatuses, methods and systems for reducing the sulfur content of coal. In one embodiment, a method for reducing the sulfur content of coal comprises the following steps. Coal is loaded into an apparatus comprising a vertically rotatable drum within a housing. The rotatable drum comprises a perforated cylindrical outer wall, a solid cylindrical inner wall, and a perforated, cylindrical central wall positioned between the outer wall and the inner wall, wherein the coal is loaded into a coal wash annulus between the central wall and the outer wall. A microbial wash fluid flows into a wash fluid annulus between the inner wall and the central wall, wherein the microbial wash fluid contains at least one of sulfur digesting bacteria and nutrients for the bacteria. The sulfur digesting bacteria and nutrients for the bacteria can be applied together or separately. The drum is rotated to cause the microbial wash fluid to migrate from the wash fluid annulus through the coal in the coal wash annulus and collect in a splash wash annulus between the outer wall and the housing.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a top view of a coal cleaning apparatus embodiment constructed in accordance with the inventive concepts disclosed herein.

FIG. 2A is a perspective view of a coal cleaning apparatus with an enclosed inner compartment and wash fluid annulus.

FIG. 2B is a top view of a coal cleaning apparatus with an enclosed interior.

FIG. 2C is a sectional view of a coal cleaning apparatus with an enclosed interior.

FIG. 3 is a perspective view of a perforated coal bin portion of a coal cleaning apparatus showing the bottom portion enclosed.

FIG. 4 is a perspective view of a coal cleaning apparatus embodiment constructed in accordance with the inventive concepts disclosed herein.

DETAILED DESCRIPTION

Before explaining at least one embodiment of the inventive concepts disclosed herein in detail, it is to be understood that the inventive concepts are not limited in their application to the details of construction, experiments, exemplary data, and/or the arrangement of the components set forth in the following description, or illustrated in the drawings. The presently disclosed and claimed inventive concepts are capable of other embodiments or of being practiced or carried out in various ways. Also, it is to be understood that the phraseology and terminology employed herein is for purposes of description only and should not be regarded as limiting in any way.

In the following detailed description of embodiments of the inventive concepts, numerous specific details are set forth in order to provide a more thorough understanding of the inventive concepts. However, it will be apparent to one of ordinary skill in the art that the inventive concepts within the disclosure may be practiced without these specific details. In other instances, well-known features have not been described in detail to avoid unnecessarily complicating the instant disclosure.

Further, unless expressly stated to the contrary, “or” refers to an inclusive or and not to an exclusive or. For example, a condition A or B is satisfied by any one of the following: A is true (or present) and B is false (or not present), A is false (or not present) and B is true (or present), and both A and B are true (or present).

In addition, use of the “a” or “an” are employed to describe elements and components of the embodiments herein. This is done merely for convenience and to give a general sense of the inventive concepts. This description should be read to include one or at least one and the singular also includes the plural unless it is obvious that it is meant otherwise.

Finally, as used herein, any reference to “one embodiment” or “an embodiment” means that a particular element, feature, structure, or characteristic described in connection with the embodiment is included in at least one embodiment. The appearances of the phrase “in one embodiment” in various places in the specification are not necessarily all referring to the same embodiment.

In general methods, devices, and systems are provided for removing sulfur from coal. In one embodiment, a method for reducing the sulfur content of coal comprises the following steps. Referring now to FIG. 1 through FIG. 4, coal is loaded into a coal cleaning apparatus 10 comprising a vertically rotatable drum 12 within a housing 14. The coal is washed with a microbial wash fluid containing sulfur digesting bacteria and nutrients for the bacteria. The drum 12 is rotated to cause the microbial wash fluid to migrate through the coal particles and into pores of the particles.

The rotatable drum 12 comprises a perforated cylindrical outer wall 16, a substantially solid cylindrical inner wall 18, and a perforated, cylindrical central wall 20 positioned between the outer wall 16 and the inner wall 18, wherein the coal is loaded into a coal wash annulus 22 between the central wall and the outer wall. A microbial wash fluid flows into a wash fluid annulus 24 between the inner wall and the central wall, wherein the microbial wash fluid contains sulfur digesting bacteria and nutrients for the bacteria. The drum is rotated to cause the microbial wash fluid to migrate from the wash fluid annulus 24 through the coal in the coal wash annulus 22 and collect in a splash wash annulus 26 between the outer wall 16 and the housing 14. Coal can be removed from the coal cleaning apparatus 10 using conventional designs and equipment.

In one embodiment, at least one of the perforated cylindrical outer wall 16 and the perforated cylindrical central wall 20 comprise a double wall wherein both walls are perforated. In an open position, the perforations overlap and fluids can flow from one side of the cylindrical wall to the other side through the perforations. In a closed position, the perforations do not overlap and fluids cannot flow from and one side of the cylindrical wall to the other side through the perforations. Suitable designs are known to those skilled in the art and include double walls that can be rotated relative to each other or moved vertically relative to each other to cover or uncover the perforations.

It is anticipated that the centrifugal force from rotating the coal in the rotatable drum 12 will cause horizontal migration of the microbial wash fluids and will cause the water and bacteria to better penetrate the pores and crevices of the coal particles. This can be further assisted by vibrating the coal in the rotatable drum 12. For example, walls of the housing 14 or the perforated cylindrical outer wall 16 can be caused to vibrate by attaching metal bar vibrators.

The rotational speed or rpm of the rotatable drum 12 depends in part on the diameter of the apparatus 10. The housing 14 is typically stationary, although in some designs the housing 14 may be fixed to the rotatable drum and rotate with it. Rotation of the drum is achieved using, for example, an electric motor.

As shown in FIG. 1, reinforcing bars 30 can be utilized to help stabilize the rotatable drum 12. In one embodiment, the reinforcing bars 30 extend radially from a center of the rotatable drum across at least an upper portion of the wash fluid annulus 24. Reinforcing bars can also extend radially from a center of the rotatable drum across a bottom portion of the wash fluid annulus 24. In one embodiment, reinforcing bars 30 along the upper portion of the wash fluid annulus 24 are also used as a means of water delivery. In yet another embodiment (not shown), the reinforcing bars 30 extend over the coal wash annulus 24 and include spray nozzles or the like for distributing water or microbial fluids over the coal.

In one embodiment, the addition of bacteria and nutrients is staged. The fluid containing bacterial nutrients is first circulated through the coal. The coal is then drained by “centrifuging” in the rotatable drum and dried with air or warmed air. The inner compartment 28 and the wash fluid annulus 26 are enclosed as shown in FIG. 2A through FIG. 2C and air is added to the inner compartment 28. The air can be recirculated and an odor-removal step can be incorporated. Air pressure caused by addition of air to the inner compartment 28 forces the air through the coal thereby drying the surface of the coal and leaving the nutrients on the surfaces including pores and crevices of the coal particles. The bacteria can then be added to the coal and will utilize the nutrients on the coal surfaces, pores and crevices to multiply while digesting the sulfur present. In one embodiment, bacteria are added with water warmed to a temperature in the range of about 80° F. to 140° F. The warm water encourages increased microbial activity.

Suitable strains of sulfur-digesting bacteria are known by those skilled in the art. For example, thiophilic bacteria such as thiobacillus ferrooxidans and sulfolobus acidocaldarius remove pyrite from coal by oxidizing pyritic sulfur to soluble sulfates. U.S. Pat. No. 4,562,156 to Isbister et al. describes a mutant microorganism Pseudomonas sp. CB1 (ATCC 39381) used in the removal of organic sulfur compounds from carbonaceous materials including coal.

Bacterial nutrients typically contain a source of nitrogen and phosphorus. Suitable examples include potassium phosphate and ammonium sulfate. In one embodiment, chicken waste is used to provide the bacterial nutrients.

In one embodiment, the coal cleaning apparatus 10 is located at or adjacent a coal mine or a coal burning power plant. The sulfur content of the coal is significantly reduced before the coal is removed from the coal cleaning apparatus 10.

In one embodiment, the coal cleaning apparatus 10 is located at or adjacent the coal mine. The coal is contacted with the microbial wash fluid containing sulfur digesting bacteria and nutrients for the bacteria while rotating the drum 12. The coal is removed from the coal cleaning apparatus 10 along with the microbial wash fluid for transportation to a power plant. The sulfur digesting bacteria remove at least a portion of coal's sulfur content during transportation. Nonlimiting examples of modes of transportation include, but are not limited to, rail and pipeline. By using the transportation vehicle as a reactor, the size and cost of the coal cleaning apparatus 10 is greatly reduced.

In summary, a method for reducing the sulfur content of coal is presented, comprising the steps of: loading the coal into a coal cleaning apparatus 10 comprising a vertically rotatable drum 12 within a housing 14, the rotatable drum 12 comprising a perforated cylindrical outer wall 16, a cylindrical inner wall 18, and a perforated, cylindrical central wall 20 positioned between the outer wall 16 and the inner wall 18, wherein the coal is loaded into a coal wash annulus 22 between the central wall 20 and the outer wall 16; introducing a microbial wash fluid into a wash fluid annulus 24 between the inner wall 28 and the central wall 20, wherein the microbial wash fluid contains sulfur digesting bacteria and nutrients for the bacteria; rotating the drum 12 to cause the microbial wash fluid to migrate from the wash fluid annulus 24 through the coal in the coal wash annulus 22 and collect in a splash wash annulus 26 between the outer wall 16 and the housing 14; and removing the coal from the coal cleaning apparatus, wherein the sulfur content of the coal is reduced.

In one embodiment, the rotatable drum further comprises reinforcing bars extending radially from a center of the rotatable drum across an upper portion of the wash fluid annulus.

In one embodiment, a method for reducing the sulfur content of coal, comprises the steps of: loading the coal into a coal cleaning apparatus 10 comprising a vertically rotatable drum 12 within a housing 14, the rotatable drum 12 comprising a perforated cylindrical outer wall 16, a cylindrical inner wall 18, and a perforated, cylindrical central wall 20 positioned between the outer wall 16 and the inner wall 18, wherein the coal is loaded into a coal wash annulus 22 between the central wall 20 and the outer wall 16; introducing a wash fluid into a wash fluid annulus 24 between the inner wall 28 and the central wall 20, wherein the wash fluid contains bacterial nutrients including a source of nitrogen and phosphorus; rotating the drum 12 to cause the wash fluid to migrate from the wash fluid annulus 24 through the coal in the coal wash annulus 22 and collect in a splash wash annulus 26 between the outer wall 16 and the housing 14; introducing a microbial wash fluid into the wash fluid annulus 24, wherein the microbial wash fluid contains sulfur digesting bacteria; rotating the drum 12 to cause the microbial wash fluid to migrate from the wash fluid annulus 24 through the coal in the coal wash annulus 22 and collect in a splash wash annulus 26 between the outer wall 16 and the housing 14; and removing the coal from the coal cleaning apparatus, wherein the sulfur content of the coal is reduced. Optionally, the rotatable drum further comprises reinforcing bars extending radially from a center of the rotatable drum across an upper portion of the wash fluid annulus.

In one embodiment, a method for reducing the sulfur content of coal, comprising the steps of: loading the coal into a coal cleaning apparatus 10 comprising a vertically rotatable drum 12 within a housing 14, the rotatable drum 12 comprising a perforated cylindrical outer wall 16, a cylindrical inner wall 18, and a perforated, cylindrical central wall 20 positioned between the outer wall 16 and the inner wall 18, wherein the coal is loaded into a coal wash annulus 22 between the central wall 20 and the outer wall 16; introducing a microbial wash fluid into a wash fluid annulus 24 between the inner wall 28 and the central wall 20, wherein the microbial wash fluid contains sulfur digesting bacteria and nutrients for the bacteria; removing the coal and the microbial wash fluid from the coal cleaning apparatus; and allowing the bacteria to digest the sulfur during transportation or storage of the coal.

In one embodiment, the coal cleaning apparatus 10 is located at or adjacent the coal mine. Coal is loaded into the coal cleaning apparatus and contacted with microbial wash fluid containing bacteria nutrients while rotating the drum 12 with the perforated cylindrical outer wall 16 in a closed position. The perforated cylindrical outer wall 16 is then shifted to an open position, aligning the perforations and allowing the coal to drain. The coal is optionally air dried before removing from the coal cleaning apparatus 10. The removed coal is slurried with a warmed aqueous solution containing sulfur digesting bacteria and transported to a power plant. The sulfur digesting bacteria remove at least a portion of coal's sulfur content during transportation.

From the above descriptions, it is clear that the presently disclosed and claimed inventive concepts are well-adapted to carry out the objects and to attain the advantages mentioned herein, as well as those inherent in the presently disclosed and claimed inventive concept. While the presented embodiments have been described for purposes of this disclosure, it will be understood that numerous changes may be made which will readily suggest themselves to those skilled in the art and which are accomplished within the spirit of the presently disclosed and claimed inventive concepts. 

What is claimed is:
 1. A method for reducing the sulfur content of coal, comprising the steps of: loading the coal into a coal cleaning apparatus comprising a vertically rotatable drum within a housing, the rotatable drum comprising a perforated cylindrical outer wall, a cylindrical inner wall, and a perforated, cylindrical central wall positioned between the outer wall and the inner wall, wherein the coal is loaded into a coal wash annulus between the central wall and the outer wall; introducing a microbial wash fluid into a wash fluid annulus between the inner wall and the central wall, wherein the microbial wash fluid contains sulfur digesting bacteria and nutrients for the bacteria; rotating the drum to cause the microbial wash fluid to migrate from the wash fluid annulus through the coal in the coal wash annulus and collect in a splash wash annulus between the outer wall and the housing; and removing the coal from the coal cleaning apparatus, wherein the sulfur content of the coal is reduced.
 2. The method of claim 1, wherein the rotatable drum further comprises reinforcing bars extending radially from a center of the rotatable drum across an upper portion of the wash fluid annulus.
 3. A method for reducing the sulfur content of coal, comprising the steps of: loading the coal into a coal cleaning apparatus comprising a vertically rotatable drum within a housing, the rotatable drum comprising a perforated cylindrical outer wall, a cylindrical inner wall, and a perforated, cylindrical central wall positioned between the outer wall and the inner wall, wherein the coal is loaded into a coal wash annulus between the central wall and the outer wall; introducing a wash fluid into a wash fluid annulus between the inner wall and the central wall, wherein the wash fluid contains bacterial nutrients including a source of nitrogen and phosphorus; rotating the drum to cause the wash fluid to migrate from the wash fluid annulus through the coal in the coal wash annulus and collect in a splash wash annulus between the outer wall and the housing; introducing a microbial wash fluid into the wash fluid annulus, wherein the microbial wash fluid contains sulfur digesting bacteria; rotating the drum to cause the microbial wash fluid to migrate from the wash fluid annulus through the coal in the coal wash annulus and collect in a splash wash annulus between the outer wall and the housing; and removing the coal from the coal cleaning apparatus, wherein the sulfur content of the coal is reduced.
 4. The method of claim 3, wherein the rotatable drum further comprises reinforcing bars extending radially from a center of the rotatable drum across an upper portion of the wash fluid annulus.
 5. A method for reducing the sulfur content of coal, comprising the steps of: loading the coal into a coal cleaning apparatus comprising a vertically rotatable drum within a housing, the rotatable drum comprising a perforated cylindrical outer wall, a cylindrical inner wall, and a perforated, cylindrical central wall positioned between the outer wall and the inner wall, wherein the coal is loaded into a coal wash annulus between the central wall and the outer wall; introducing a microbial wash fluid into a wash fluid annulus between the inner wall and the central wall, wherein the microbial wash fluid contains sulfur digesting bacteria and nutrients for the bacteria; removing the coal and the microbial wash fluid from the coal cleaning apparatus; and allowing the bacteria to digest the sulfur during transportation or storage of the coal. 